FRIDAY, March 29 (HealthDay News) -- People with untreated depression may not gain the full benefits of certain healthy lifestyle habits, according to a new study.

The anti-inflammatory effects typically associated with exercise and light to moderate alcohol consumption may be hindered by depression, the Duke Medicine researchers said.

They added that their findings suggest another potential danger of depression, which affects about 1 in 10 adults in the United States.

For the study, the researchers looked at the exercise levels and alcohol consumption of more than 200 nonsmoking, healthy adults with no history or diagnosis of mental illness. Screening tests revealed, however, that 4.5 percent of the participants met the criteria for depression.

The researchers also analyzed levels of C-reactive protein (CRP) in blood samples collected from the participants. CRP is used to predict future risk of heart disease and other chronic inflammatory conditions, and may also play a role in the formation of plaque that accumulates in arteries.

Previous research has shown that exercise and moderate alcohol consumption -- defined as one drink a day for women and two a day for men -- can reduce inflammation and lower the risk of heart disease and type 2 diabetes. In contrast, diabetes is associated with higher CRP levels and increased risk of heart disease and diabetes.

Participants in this study who were physically active generally had lower CRP levels, with the exception of those with depression. The researchers also found that light to moderate alcohol consumption was associated with lower CRP levels in men who were not depressed, but not in those with depression.

Among women, depression did not have much effect on CRP levels in those who didn't drink, drank occasionally or were light to moderate drinkers, according to the study, published online March 26 in the journal Brain, Behavior, and Immunity.

"Our findings suggest depression not only directly affects an individual's mental and physical health but it also might also diminish the health benefits of physical activities and moderate alcohol consumption," lead author Edward Suarez, an associate professor of psychiatry and behavioral sciences, said in a Duke Medicine news release.

"This appears to be specific to inflammation, which we know increases the risk for heart disease, so our findings suggest that depression could be a complicating risk factor," he added.

The findings could prove important to doctors when deciding how best to help patients reduce their risk of heart disease and type 2 diabetes. Although the research showed an association between depression and diminished returns on healthy lifestyle habits, it did not prove a cause-and-effect relationship.